The compound (Z)—O-octadec-9-en-1-yl O,O-dihydrogen phosphorothioate (hereafter designated “Rx100” for the interest of simplicity), a lysophosphatidic acid (“LPA”) receptor agonist and/or antagonist, may enhance cell proliferation, treat wound healing, or protect tissues such as those of the gastrointestinal and hematopoietic systems against chemotherapeutic- or radiation-induced apoptosis. See, for example, U.S. Pat. Nos. 7,217,704 and 7,947,665. The Formula I below represents the structure of the Rx100 free acid (“Rx100.FA”):

Pharmaceutical compound may exist in many different forms, for example, free base, free acid, various salts, liquid, crystalline solid, hydrate, solvate, amorphous or polymorphous forms. Variations of physical forms may often cause variations of stability, solubility, bioavailability, filterability, scalability, pharmacokinetics and/or bioequivalency of a pharmaceutical compound. It is therefore desirable to make a pharmaceutical compound in a desirable form.
Rx100.FA is a pale yellow oily substance. In addition to being in a less desirable oil form it has a thiol type odor, needs storage at less than −20° C. to preserve short-term stability, has poor solubility in water, and is difficult to handle for practical purposes. Attempts to form more desirable salt forms such as the sodium or potassium salts failed to yield filterable solids.
Treatment of Rx100.FA solution in methanol with 3 equivalents of ammonia forms a precipitate which upon freeze-drying provides an Rx100.Ammonia salt powder. However, Rx100.Ammonia salt also has many undesirable features. For example, (i) ammonia may be lost during storage; ii) the salt may absorb moisture during routine handling procedures by the formation of a stick mass; iii) formation of the salt does not exclude impurities (as opposed to crystallization); and iv) additives, stabilizers found in solvents, synthesis impurities and by products may get incorporated in the drug solid during salt formation. Therefore, there is an urgent need to obtain a new Rx100 salt in an improved form with more desirable features.